docs: def get_subgraph_by_annotation_value(graph, annotation, values):
      """Induce a sub-graph over all edges whose annotations match the given key and value.
  
      :param pybel.BELGraph graph: A BEL graph
      :param str annotation: The annotation to group by
      :param values: The value(s) for the annotation
      :type values: str or iter[str]
      :return: A subgraph of the original BEL graph
      :rtype: pybel.BELGraph
      """
      if isinstance(values, str):
          values = {values}
  
      return get_subgraph_by_annotations(graph, {annotation: values})